Useful and freaky

OK, sometimes a thing is just plain wierd, grabs you viscerally and makes you say "huh?"... and sometimes a thing is a useful manipulation of visual imagery that allows you to instantly grasp a very complicated quantitative concept. And sometimes, it's both!

There are a number of examples of anatomical homunculi (pleural of homunculus, Latin for "little man"), used to illustrate the relative sensory and motor real estate in the brain assigned to the various body parts. The hands and face require much more precise control of movement than, say, the legs. These areas also have much better sensory discrimination. Because of this, they require more motor and sensory neurons in the brain, and therefore they are proportionally bigger in the homunculus.

This concept has been around for decades, but usually just as a crude drawing. The natural history museum in London has two terrific three dimensional renderings of these little guys- here is the motor version, and here is the sensory version.


For those of you who google reflexively, the term homunculus has other usage as well. Initially a homunculus was a legendary manmade assistant to alchemists (starting in 16th century Switzerland with the infamous Paracelsus). Various recipies for making these creatures were described, usually involving human semen. Later, the concept was used to visualize a miniature human inside each individual sperm, in one of the early theories of conception.

Interesting, huh? Sure beats sifting through votes in Ohio like all the other blggers...